Wikipedia does not support certificate login, so I cannot log in using my X.509 certificate (in fact Wikipedia does not even offer SSL encryption, so my password could be sniffed by a man in the middle!).

Wikipedia could run its own Certification Authority and give higher status to users who provide the kind of information that CAs traditionally require in order to obtain a Class 2 certificate (e.g., government-issued photo IDs and notarized documents).

Wikipedia could regularly ask users to verify the content on their own user pages, taking a digitally signed or encrypted email response with verification as approval.

Wikipedia could do any and all of these things. If they did, then Wikipedia could really know who is creating the content at Wikipedia. But it doesn't. So instead, we don't know who creates the content at Wikipedia, whether the people who run Wikipedia are who they claim to be, or whether Wikipedia has any reliability whatsoever.